The present invention relates generally to a zoom optical system and electronic equipment incorporating the same, and more specifically to a compact zoom optical system and electronic equipment that incorporates the same. Such electronic equipments, for instance, include digital cameras, video cameras, digital video units, personal computers, mobile computers, cellular phones, and personal digital assistants.
Recently, personal digital assistants abbreviated as PDAs and cellular phones have boasted explosive growth in demand. Added to some such equipments are a digital camera function and a digital video function. To implement those functions, CCD (charge coupled device) and CMOS (complementary metal oxide semiconductor) sensors are now in use. To reduce the sizes of such equipments, it is preferable to rely on an image pickup device having a relatively small effective area on a receiving plane. This requires a sensible tradeoff between compactness and low cost while keeping the performance of an optical system high. Patent Publications 1, 2 and 3 referred to below disclose prior art zoom optical systems whose size and cost are reduced to some extents.
Patent Publication 1
JP(A)9-179026
Patent Publication 2
JP(A)10-333034
Patent Publication 3
JP(A)10-48524
However, the zoom optical system set forth in Patent Publication 1 leaves much to be desired in terms of size reductions thanks to the third lens group comprising two lenses. A problem with the zoom optical system described in Patent Publication 2 is that large lens thickness renders the length of the lens system long because of using a gradient index lens in the second lens group.
In the zoom optical system shown in Patent Publication 3, too, there is left a great deal to be desired in terms of compactness because an aperture stop is interposed between the second lens group and the third lens group and so more lenses is needed for correction of chromatic aberration of magnification.